Re: 555 timer problem

On 29 Sep 2006 03:38:51 -0700, "randomname"
<randomname12345@xxxxxxxxx> wrote:

Wow! Thank you so much for providing me with all of these ideas. Ive
looked into the "positive displacement pump" solution and found just
the companies who might be able to help me out.. I just hope the cost
isn't absurd.

This page may contain the pump I'm looking for:
http://www.micropump.com/products/pumps/gear/

Yeah that looks like it (or its many cousins) could work.

Since you seem to be playing with 555's and battery power, I figured
this was more of a project to satisfy curiosity or for self
satisfaction (low budget toy).

And chemical metering pumps do tend to be expensive. They are made
for chemical, pharmaceutical, industrial applications and those people
have lots of money - and it ain't exactly a common item. They want
absolute accuracy, a pump that will run for a long time before
repairing, and usually in a harsh environment - that costs.

Farmers use them too, for fertilizer and livestock applications - but
it is still in a business context although they have less to spend.
Farm pumps are likely to be high volume types.

There the savings is usually one of chemicals that have a long life
when in a "stock" concentration and very short life when in a
"working" solution/dilution - the solution to the problem is mix the
two just before applying them.

What cost is absurd?

I haven't been following the whole thread, so I haven't kept up with
your quest. I was off for a week with the wife too . . . Is this,
are you building a water clock?

I had a deal where I had to fill and empty flasks in a robotic
chemical assay application. I found a really slick pump to do the
fill. Had to be within a fraction of a percent to volume.
Pharmaceutical company and money is no object (unless, of course, I
asked for a raise). Well anyhow this pump used compressed air on one
side of a piston and liquid to be pumped on the other. A stop (bolt
that ran into the end) adjusted the stroke length and delivery volume.
Very accurate and virtually foolproof and maintenance free. Looks
like it was made from schedule 80 PVC plumbing parts, with a little
machining and hardware. Check valves were off the shelf parts - one
way ball checks. Ingenuous and expensive but did the job
beautifully.

Another thought for accuracy and cheap easy to make (but not pulse
free) are peristaltic pumps. A hub spins with a motor. The hub has
rollers around the periphery. A piece of tubing is stretched around
~180 to ~270 degrees of arc against the rollers with enough force to
close the tubing where it touches the rollers (only works with low
modulus(?) tubing like silicone). I was using one to fill vials with
a 600 RPM drive and filled the vials to within a tenth of a percent,
using timing to turn the pump on and off.

You mentioned something about viscosity and drop size? I was a kid
and watching TV in the 50's sometime. There was a show called "You
Asked for It." Someone wanted to know what the largest drop size
was, and they sure produced a prodigious drop. They showed people
climbing up a ladder and dumping buckets into this large (6-8 foot
diameter) ring with about a three foot height. The "drop" formed at
the bottom of the ring and went into a huge tub.

Well this thing, if my memory is right, was just a ring with a very
fine mesh screen at the bottom and a layer of cloth resting on the
screen. They had to start it off carefully by wetting the cloth until
they had a few inches of water in it then just dumped buckets in it
until it drop 'd through the screen. You could see the drop forming
long before it dropped and it looked like it held a few hundred
gallons. The ring was formed with a "bell" opening where they were
pouring water, and it looked like the drop formed below with some
margin - like there was a rim or something that prevented the drop
from going out to the edge of the ring.

That was a long time ago. I was a kid. It was a black and white TV
and on an antenna - so perhaps there are gaps in my memory.

They didn't say, or I don't remember, if they had any way to increase
the surface tension of the water - I think not. I think the whole
idea/experiment was predicated on the same idea as used by aerators on
faucets.

Before someone jumps in my *** - aerators work mostly by keeping air
out of the pipe after the water is shut off - no air no drip (unless
the washer is bad). They also entrain air into the delivery for
esthetic reasons and help dissipate some off tastes that may be
present, due to volatile chemicals in the water.

I don't know if you can use that aerator thing I figure if accurate
delivery of water is paramount you don't measure by the drop, so a
drop must be necessary for a visual reason or for its impact when
falling onto something.

In absolute scientific terms a drop is a drop - but a drop at one
temperature will weigh more or less as the temperature and density
changes - if one were building a clock that needed a specific weight
for the mechanism, for instance.



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